Constraining the long-term sedimentation history at ancient Lake Cahuilla, Coachella, CA from Holocene sediment cores

Marina O. Argueta, Sourav Saha, Seulgi Moon, Nathan D. Brown, Thomas K. Rockwell, Katherine M. Scharer, Zoe Morgan, & Jenifer Leidelmeijer

Submitted September 11, 2022, SCEC Contribution #12041, 2022 SCEC Annual Meeting Poster #247

The southernmost ~100 km of the southern San Andreas fault (SSAF) has an average ground-rupturing earthquake recurrence interval of ~200 years over the last 1000 years based on published paleoseismic studies. However, the most recent ground-rupturing earthquake within this area occurred ~300 years ago, during the last highstand of the ancient Lake Cahuilla (LC) in the Salton Trough, California. The correlation between major SSAF earthquakes and LC highstands is debated and the relationship is difficult to establish due to the brevity of the records. In order to evaluate if there is a correlation between the major rupture events along the SSAF and LC highstands, an extended sediment depositional history with grain size measurements to identify LC highstands is needed. In this study, we have analyzed two continuous boreholes, 33.5 and 40 m deep, from the Coachella paleoseismic site along the SSAF. The 33.5-m-deep core was collected within a small structural depression at 9 m elevation near a ~13-m-high shoreline of LC. The 40-m-deep core was collected 135 m southwest of the first core, outside the deformation zone. From these two boreholes, we constrain the long-term sedimentation history of LC using luminescence (p-IR IRSL) dating and grain size analysis. We determine the timing and frequency of sediment supply, aggradation, and depositional hiatuses from layers in the cores. Our preliminary results show that the borehole logs extend the sedimentation history at the Coachella paleoseismic site to ≥ ~9 ka. These cores also exhibit different characteristics of sedimentary deposits, with potentially different numbers of fine grain sediment layers, potentially LC highstands. Our work from both of these boreholes contributes to the further understanding of the long-term depositional and tectonic history along the SSAF by developing an extended lake highstand chronology.

Key Words
paleoseimicity, San Andreas fault, borehole

Argueta, M. O., Saha, S., Moon, S., Brown, N. D., Rockwell, T. K., Scharer, K. M., Morgan, Z., & Leidelmeijer, J. (2022, 09). Constraining the long-term sedimentation history at ancient Lake Cahuilla, Coachella, CA from Holocene sediment cores. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
San Andreas Fault System (SAFS)